ltk_meta

Reading, editing and writing League of Legends property bins (.bin): the hierarchical, hash-keyed configuration format the game uses for almost all of its data - champions, items, UI, VFX, maps.

Two kinds of file share the .bin extension and this crate reads both:

• PROP - a tree of objects with typed properties (Bin).
• PTCH - an override bin: deletions, extra objects and property patch records applied over a base bin (BinOverride).

Public surface

Object names and property names are stored as FNV-1a hashes of the lowercased string - compute them with ltk_hash's fnv1a::hash_lower. Integer literals and hashes convert freely where a name is expected.

Reading a bin

use std::fs::File;
use ltk_meta::Bin;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut file = File::open("data.bin")?;
    let bin = Bin::from_reader(&mut file)?;

    println!("depends on: {:?}", bin.dependencies);
    for (path_hash, object) in &bin.objects {
        println!("{path_hash:08x} ({:08x}): {} properties", object.class_hash, object.properties.len());
    }

    Ok(())
}

Streaming a bin

Bin::from_reader parses everything. When you only need the object table - harvesting hashes across thousands of files, or pulling one object's facts out of a big bin - BinStream mounts the file, reads just the header, and skips object bodies by their size fields. Hand mount the bare File; buffering is internal.

use std::fs::File;
use ltk_meta::BinStream;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut stream = BinStream::mount(File::open("data.bin")?)?;
    println!("version {}, {} objects", stream.version(), stream.class_hashes().len());

    // Sweep the object table: one descriptor per object, no value parsing.
    for entry in stream.entries() {
        let entry = entry?;
        println!("{:08x}: {:08x}", entry.path_hash, entry.class_hash);
    }

    // Random access by path hash, served from the table of contents the sweep built.
    if let Some(mut object) = stream.object(0x4a47c414u32)? {
        println!("{} properties", object.property_count()?);
    }
    Ok(())
}

The entries() sweep populates a BinToc (Clone, serializable with the serde feature) as a side effect, so toc() and object(hash) after a sweep cost no further reads.

Bin::from_reader is itself BinStream::mount plus into_bin(), so the streaming surface and the eager tree are one parser and cannot drift.

Reading inside an object

Descending buffers the object's declared byte range once and views it in place. Iteration, lookup by name hash and descent into nested values are all slice arithmetic from there; nothing decodes until it is touched and nothing allocates until an owned value is asked for.

use std::fs::File;
use ltk_meta::{BinStream, ValueView};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut stream = BinStream::mount(File::open("data.bin")?)?;
    let mut objects = stream.objects();

    while let Some(mut object) = objects.next()? {
        let view = object.view()?;

        // Every string in the object, borrowed straight out of the buffer.
        for property in view.properties() {
            if let ValueView::String(text) = property?.value_view()? {
                println!("{text}");
            }
        }

        // `Elements[3].Position`, without materializing a single sibling.
        if let Some(elements) = view.property(0x1234_5678u32)? {
            if let ValueView::Container(list) = elements.value_view()? {
                if let Some(ValueView::Embedded(embed)) = list.get(3)? {
                    println!("{:?}", embed.property(0x9abc_def0u32)?.map(|p| p.kind()));
                }
            }
        }
    }
    Ok(())
}

ObjectStream::read() gives the owned BinObject instead, and BinStream::cached_object() resolves through an installed ObjectCache (NoCache by default, LruObjectCache shipped) and hands back an Arc. ObjectStream::byte_range() gives the object's extent in the file, for copying one out verbatim.

Asking what a value is without reading it

A complex value declares its shape in the few header bytes ahead of its body, so a PropertyView can say what it holds - and how many - at skip cost, without descending. shape() returns the same ValueShape the resolver's type rule uses, so "is this a Container[ObjectLink]?" is one comparison rather than a parse.

use std::fs::File;
use ltk_meta::{BinStream, PropertyKind};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut stream = BinStream::mount(File::open("data.bin")?)?;
    let mut objects = stream.objects();

    while let Some(mut object) = objects.next()? {
        let view = object.view()?;

        for property in view.properties() {
            let property = property?;
            let shape = property.shape()?;

            // Every list of object links, and how long each one is.
            if shape.kind == PropertyKind::Container && shape.item_kind == Some(PropertyKind::ObjectLink) {
                // e.g. `1a2b3c4d: Container[ObjectLink] of Some(12)`
                println!("{:08x}: {shape} of {:?}", property.name_hash(), property.item_count()?);
            }
        }
    }
    Ok(())
}

item_count() answers for containers and maps and is None for everything else, an option included - whether an option holds anything is OptionalView::is_some.

Legacy kind numbering

Bins written before WadChunkLink existed number the complex kinds one lower. A handle mounts as Numbering::Current and stays there until it meets a kind byte that only decodes as Numbering::Legacy: that object is re-walked from the bytes already in memory, and the handle is latched for the rest of its life. Nothing is re-read, and a genuinely desynced file can be reinterpreted this way rather than reported as broken - so numbering() is how to tell it happened.

use std::fs::File;
use ltk_meta::{BinStream, Numbering};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut stream = BinStream::mount(File::open("data.bin")?)?;
    let mut objects = stream.objects();

    while let Some(mut object) = objects.next()? {
        object.view()?;
    }

    if stream.numbering() == Numbering::Legacy {
        println!("this file was written before WadChunkLink existed");
    }
    Ok(())
}

A view carries the numbering it was built under, so one handed out before the flip keeps reading the way it started.

Opening many objects at once

object(hash) answers one question per seek. objects_batch takes the whole request up front, so a cold handle resolves it during one forward scan that stops at the last hit, and a warm one visits the rows in offset order. Yield order is file order; missing() reports the hashes the file does not hold.

use std::fs::File;
use ltk_meta::BinStream;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut stream = BinStream::mount(File::open("data.bin")?)?;
    let mut batch = stream.objects_batch([0x4a47c414u32, 0x1a2b3c4du32]);

    while let Some(mut object) = batch.next()? {
        println!("{:08x}: {} properties", object.path_hash(), object.property_count()?);
    }
    println!("not in this bin: {:?}", batch.missing());
    Ok(())
}

Walking a bin

ltk_meta::walk is one traversal for both trees. The walk calls a Visitor once per node of an object, in pre-order and file order, and once for every property, leaves included, before it descends. The visitor answers a Visit that continues, prunes a property, stops or aborts. The visitor is generic over the tree: the same Census runs over an owned Bin and over a BinStream, where the walk materializes nothing.

use ltk_hash::BinHash;
use ltk_meta::{
    walk::{Node, TreeValue, Visit, Visitor},
    Error,
};

/// Counts nodes and records the address of every `Struct` of one class.
#[derive(Default)]
struct Census {
    nodes: usize,
    hits: Vec<(BinHash, String)>,
}

impl<'a, V: TreeValue<'a>> Visitor<'a, V> for Census {
    type Error = Error;

    fn enter_node(&mut self, node: &Node<'_, 'a, V>) -> Result<Visit, Error> {
        self.nodes += 1;
        if *node.class_hash() == 0x1e6b_a0c4 {
            self.hits.push((node.object_hash(), node.trail().to_string()));
        }
        Ok(Visit::Continue)
    }
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let bin = ltk_meta::Bin::from_reader(&mut std::fs::File::open("data.bin")?)?;
    let mut census = Census::default();
    bin.walk(&mut census)?;
    println!("{} nodes, {} hits", census.nodes, census.hits.len());

    let mut stream = ltk_meta::BinStream::mount(std::fs::File::open("data.bin")?)?;
    let mut census = Census::default();
    stream.walk(&mut census)?;
    Ok(())
}

In parallel. The walk over one object is sequential by contract: one visitor, pre-order, Stop and Skip as ordered decisions. Objects are independent of one another, and every view, node and trail type is Send. A sweep parallelizes across objects with one visitor instance per worker and a reduce at the end. Nothing in the crate schedules this. The split is the caller's.

let objects: Vec<_> = bin.objects.values().collect();
let workers = std::thread::available_parallelism().map_or(1, |n| n.get());
let per_worker = objects.len().div_ceil(workers).max(1);

let counted = std::thread::scope(|scope| {
    let workers: Vec<_> = objects
        .chunks(per_worker)
        .map(|chunk| {
            scope.spawn(move || {
                let mut census = Census::default();
                for object in chunk {
                    object.walk(&mut census)?;
                }
                Ok::<_, Error>(census)
            })
        })
        .collect();

    let mut all = Census::default();
    for worker in workers {
        let census = worker.join().expect("a worker panicked")?;
        all.nodes += census.nodes;
        all.hits.extend(census.hits);
    }
    Ok::<_, Error>(all)
})?;

println!("{} nodes, {} hits", counted.nodes, counted.hits.len());

Across many files the same shape applies one level up: one task per file, each mounting its own BinStream and walking it sequentially. The per-object walk is microseconds. Decompression and I/O are where a sweep spends its time.

Editing and saving

walk::VisitorMut runs the same traversal over an owned object through &mut: a node callback edits the node's properties, a property callback edits or replaces the value, and the trail is the read-only walk's. BinDelta holds whole-object edits against a mounted BinStream, and BinStream::write_patched writes the file with them applied: it copies every object the delta does not name byte for byte, and encodes only the edited ones.

use ltk_hash::{BinHash, Hash as _};
use ltk_meta::{
    property::values,
    walk::{PropertyRefMut, Visit, VisitorMut},
    BinDelta, BinStream, Error, PropertyValueEnum,
};

const NAME: BinHash = BinHash(0x0000_0002);

/// Rewrites every `String` under one field as the hash of its text.
#[derive(Default)]
struct Rehash {
    changed: usize,
}

impl VisitorMut for Rehash {
    type Error = Error;

    fn enter_property(&mut self, property: &mut PropertyRefMut<'_>) -> Result<Visit, Error> {
        if property.field() != NAME {
            return Ok(Visit::Continue);
        }
        let PropertyValueEnum::String(text) = property.value() else {
            return Ok(Visit::Continue);
        };
        let hash = values::Hash::new(BinHash::hash_str(&text.value));
        *property.value_mut() = hash.into();
        self.changed += 1;
        Ok(Visit::Continue)
    }
}

let mut stream = BinStream::mount(std::fs::File::open("data.bin")?)?;
let mut delta = BinDelta::new();

let mut objects = stream.objects_batch([0x1111_0001u32]);
while let Some(mut object) = objects.next()? {
    let mut object = object.read()?;
    let mut rehash = Rehash::default();
    object.walk_mut(&mut rehash)?;
    if rehash.changed > 0 {
        delta.replace(object);
    }
}

let mut out = Vec::new();
stream.write_patched(&delta, &mut out)?;

A handle latched onto the legacy kind numbering refuses the delta. into_bin() and Bin::to_writer transcode the whole file instead.

Creating one programmatically

Build a tree with the builder, or the simple constructor:

use ltk_meta::{property::values, Bin, BinObject};

fn main() {
    let bin = Bin::builder()
        .dependency("common.bin")
        .object(
            BinObject::builder(0x12345678u32, 0xABCDEF00u32) // (path hash, class hash)
                .property(0x1111, values::I32::new(42))
                .property(0x2222, values::String::from("hello"))
                .build(),
        )
        .build();

    assert_eq!(bin.objects.len(), 1);
}

Complex values are validated at construction - container items must share one kind, map keys must be a kind that can key a map - so Map::new and friends return Result:

use ltk_meta::{property::values, PropertyKind};

fn main() -> Result<(), ltk_meta::Error> {
    let list = values::Container::from(vec![values::I32::new(1), values::I32::new(2)]);
    let map = values::Map::new(
        PropertyKind::U32,
        PropertyKind::String,
        vec![(values::U32::new(7).into(), values::String::from("seven").into())],
    )?;

    assert_eq!(list.len(), 2);
    assert_eq!(map.entries().len(), 1);
    Ok(())
}

Editing and writing back

use std::fs::File;
use std::io::Cursor;
use ltk_meta::{Bin, BinObject};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut bin = Bin::from_reader(&mut File::open("data.bin")?)?;

    bin.add_object(BinObject::new(0x11112222, 0x33334444));
    bin.remove_object(0x55556666);

    let mut output = Cursor::new(Vec::new());
    bin.to_writer(&mut output)?;
    Ok(())
}

Round-tripping is a design goal: reading a shipped bin and writing it back reproduces it byte for byte.

Addressing a property by path

PropertyPath is the language a patch record uses to name what it overrides, and it works on any object: . steps into structs and embeds, [n] indexes containers, {key} looks up map entries.

use std::fs::File;
use ltk_meta::{path::PropertyPath, property::values, Bin};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut bin = Bin::from_reader(&mut File::open("uibase.bin")?)?;
    let anchor = PropertyPath::new("Position.Anchors.Anchor")?;

    println!("{:?}", bin.resolve(0x4a47c414_u32, &anchor)?);

    // `patch` follows the client's type rule: the shape has to match, or nothing changes.
    bin.patch(
        0x4a47c414_u32,
        &anchor,
        values::Vector2::new(glam::Vec2::new(0.0, 1.0)).into(),
    )?;
    Ok(())
}

resolve_mut is the unchecked way in: it hands back a ValueSlot on whatever is there and applies no type rule, where patch reproduces the client's. The slot carries the kind its holder pins the value to - a container declares its item kind once, ahead of the values, so set refuses a value of another kind there. Editing in place through as_mut needs no check at all, because it cannot change the kind.

use std::fs::File;
use ltk_meta::{path::PropertyPath, property::ValueMut, Bin};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut bin = Bin::from_reader(&mut File::open("uibase.bin")?)?;
    let mut slot = bin.resolve_mut(0x4a47c414_u32, &PropertyPath::new("Elements[0]")?)?;

    println!("pinned to {:?}", slot.pinned_kind()); // whatever the list declared its items to be

    if let ValueMut::I32(count) = slot.as_mut() {
        count.value += 1;
    }
    Ok(())
}

Override bins (PTCH)

A patch only means something over the bin it patches. apply lays it over one in the order the client does, and reports what it could not apply instead of failing - which is also what the client does with a stale path. check answers the same question without touching anything, which is what to ask after a game update.

use std::fs::File;
use ltk_meta::{Bin, BinOverride};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut base = Bin::from_reader(&mut File::open("uibase.bin")?)?;
    let patch_bin = BinOverride::from_reader(&mut File::open("uiflipped.bin")?)?;

    for patch in &patch_bin.patches {
        // e.g. `4a47c414 Position.Anchors.Anchor = Vector2`
        println!("{:08x} {} = {:?}", patch.object_hash, patch.path, patch.kind());
    }

    let report = patch_bin.check(&base);
    println!("{report}"); // "109 applied (5 inserted), 0 skipped, ..."
    if report.is_clean() {
        patch_bin.apply(&mut base);
    }
    Ok(())
}

Merging and diffing

merge layers an edited bin over a base in place: the edit wins at every value it reaches, a map combines key by key, a struct or embed of the same class combines field by field, and whatever only the base holds survives. The report names every value the edit overwrote, and mismatched marks the ones whose shape differs - the mark a type migration leaves on a stale mod.

diff writes the difference as a BinOverride. A record cannot insert a map entry, change a value's shape or address a field with no name. At each of those places the diff writes one record at an ancestor holding the base merged with the edit, and reports a Lift. Applied to its base, the patch equals the merge.

use std::{collections::HashMap, fs::File};
use ltk_hash::{BinHash, Hash as _};
use ltk_meta::Bin;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let base = Bin::from_reader(&mut File::open("game.bin")?)?;
    let edited = Bin::from_reader(&mut File::open("mod.bin")?)?;

    let mut merged = base.clone();
    let report = merged.merge(&edited);
    for replaced in report.replaced.iter().filter(|r| r.mismatched) {
        println!("type changed at {replaced}");
    }

    let names = HashMap::from([(BinHash::hash_str("Size"), "Size".to_owned())]);
    let (patch, report) = base.diff(&edited, &names);
    for lift in &report.lifted {
        println!("{lift}"); // e.g. "01000001 1e6ba0c4: 2 map entries inserted"
    }

    let mut applied = base.clone();
    patch.apply(&mut applied);
    assert_eq!(applied.objects, merged.objects);
    Ok(())
}

Reading a .bin of unknown kind

The extension does not say which kind a file is, so either read it as a BinFile and match on what came back, or ask BinKind::identify_from_reader and call the reader you want - it leaves the magic in place, so the same reader can be handed straight on.

use std::fs::File;
use ltk_meta::BinFile;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    match BinFile::from_reader(&mut File::open("unknown.bin")?)? {
        BinFile::Prop(bin) => println!("{} objects", bin.objects.len()),
        BinFile::Override(patch_bin) => println!("{} patches", patch_bin.patches.len()),
    }
    Ok(())
}

Feature flags

• serde: Serialize/Deserialize on the tree, values, paths and reports (also enables it on the glam math types they carry).

Related crates

• ltk_ritobin: the human-readable text form of these bins, parsing to and from this crate's types.
• ltk_hash: the FNV-1a and xxhash functions the formats key everything by.
• ltk_wad: WAD archives, where the game's bins actually live.
• league-toolkit: umbrella crate that re-exports everything behind feature flags.

License

Licensed under the Apache License, Version 2.0.